In high speed data transmission systems, a transmitter consumes the most power in such systems. For low power applications, it is important to reduce this power consumption by the transmitter. One method to conserve power is to lower the operating voltage for the transmitter to reduce the overall power consumption. However, this does not aid in power reduction at the final stage driver, where, conventionally, current differential drivers are used because of their low susceptibility to power supply noise. For example, a typical 1 volt, 50 ohms differential driver with a termination of 100 ohms can consume around 20 mA, a relatively large amount of current. Furthermore, supporting multiple taps can lead to even more power usage.
A voltage mode driver can be used instead of a current differential driver, where the voltage mode driver may only consume 5 mA to achieve the same driver characteristics. However, typical voltage mode drivers consume more current in pre- and de-emphasis modes and are difficult to incorporate for a pre-defined number of taps. Therefore, it is desirable to provide new voltage mode drivers that allow for constant compensated impedance, e.g., by process, voltage and temperature (“PVT”) tuning, in an n-tap operation and consume less current in an n−1 tap operation. It is also desirable to provide new voltage mode drivers for an n+1 tap operation (including tri-state) with minimal skew impact.
Another problem for voltage mode drivers is that noise coupling from an adjacent channel can cause signal distortion at the receiving end of the channel. Various methods can be used to take care of noise at the design phase. However, effective techniques are not available once the design is completed. Therefore, it is desirable to provide new methods and circuits for noise cancellation.